Thorium has been in the news recently as it was suggested as a safer and more readily available element than Uranium for generating power.
Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.
Thorium produces a radioactive gas, radon-220, as one of its decay products. Secondary decay products of thorium include radium and actinium. In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years. Other isotopes of thorium are short-lived intermediates in the decay chains of higher elements, and only found in trace amounts. Thorium is estimated to be about three to four times more abundant than uranium in the Earth’s crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.
Pure thorium is a soft, lustrous silvery-white metal. If it doesn’t burst into flames first, thorium will slowly tarnish when exposed to air, becoming grey, as you see above, and then finally black in colour. Thorium is very ductile and, like all actinoids, thorium is radioactive.
|Monazite, a rare earth and thorium phosphate mineral, is the primary source of the world’s thorium|
When compared to uranium, there is a growing interest in developing a thorium fuel cycle due to its greater safety benefits, absence of non-fertile isotopes and its higher occurrence and availability.
India’s Kakrapar-1 reactor is the world’s first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core. India, which has about 25% of the world’s thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). The prototype is expected to be fully operational by 2016, after which five more reactors will be constructed. The reactor is a fast breeder reactor and uses a plutonium core rather than an accelerator to produce neutrons. As accelerator-based systems can operate at sub-criticality they could be developed too, but that would require more research. India currently envisages meeting 30% of its electricity demand through thorium-based reactors by 2050.
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